Have been floating around the forum for a few months, thought it would be time to become an active member at least

So, the questions I have to ask are this, (PS I did search, might have missed info that would answer my questions, If I did I apologize):
Stock standard CA18DET.
Lately I could smell petrol all over the show, checked under the hood and I concluded either leaky injector/s or perished O-ring seals on them
Q1: do the injectors themselves develop leaks, or is it usually the O-rings sealing the top of fuel rail and bottom in intake runner that just needs replacing? a little pool of fuel is accumulating on my intake runners and I can just see myself next to the road, car In flames.
Plus lately a little cloud of black smoke makes it's appearance under foot to the floor under boost, not much but not nice, seems it's overfuelling, also regular backfiring, depending on driving style at the moment.
If I have to replace injectors, (I do know they are 370cc, low impedance?) and am looking to up the boost to +- 1bar, will the same injector suffice? or am I looking at 400cc or 444cc injectors?
Q2: My gearbox has developed a grinding noise, it's prolly one of the ugliest sounds that have ever fallen upon my ears, not whining, a grinding noise, except when in 4'th. it still drives fine it's just making a hectic geraas, yes there is oil in the box, and the specified amount. who's arm can I turn to sell me an S13 box? if they belong to the family of chicken teeth, what box will fit the stock bell housing?
and thats it for now I think, big apologies if these questions make you yawn, let me do some more searches and if I get all my Q's A'd then i'll delete this post promptly.
Louis.